This invention relates to a liquid crystal display device. More particularly, this invention relates to a driving circuit that improves response as a luminance change time of a liquid crystal.
Response of liquid crystals represents generally the time from the application of a voltage to a liquid crystal to the acquisition of desired luminance. This response includes a rise response xcfx84r when the state changes from a voltage non-applied state to a voltage applied state and a fall response xcfx84d when the state changes from the voltage applied state to the voltage non-applied state. According to Japanese literature, xe2x80x9cThe Latest Technologies of Liquid Crystalsxe2x80x9d, p48, published by Industrial Research Association, each response can be determined from the following formula:
rise response xcfx84r=(xcex7ixc2x7d2)/(∈0xc2x7xcex94∈xc2x7V2xe2x88x92Kiixc2x7xcfx802)
fall response xcfx84d=(xcex7ixc2x7d2)/(kiixc2x7xcfx802)
where:
xcex7i: viscosity parameter (coefficient of viscosity)
d: liquid crystal cell gap
xcex94∈: dielectric anisotropy
V: applied voltage
Kii: elasticity parameter (elastic modulus)
This response formula of the liquid crystal suggests that in order to improve the response by contriving the liquid crystal material, the viscosity parameter xcex7i of the liquid crystal material needs to be made small. To improve the response from the aspect of the production process of a liquid crystal panel, the liquid crystal cell gap d needs to be reduced. To improve the response by a driving circuit, a driving voltage (a liquid crystal applied voltage) needs to be increased.
To elevate the driving voltage (the applied voltage to the liquid crystal) to a high voltage in the method explained above, a liquid crystal driving circuit for generating the driving voltage must be improved. Since the liquid crystal driving circuit generally comprises an integrated circuit, this integrated circuit must be accomplished by means of a high voltage process, and results in the high cost of production. Further, to improve the viscosity parameter of the liquid crystal and the cell gap, the production process of the liquid crystal must be changed drastically, and such a modification also results in a high cost of production.
If the cost of production of the liquid crystal driving circuit is restricted, the response of the liquid crystal cannot be improved. Even when any change occurs in the display content, the content displayed in a preceding frame is displayed as an after-image rasidual image (residual image). As a result, when a figure such as a rectangle, displayed on the liquid crystal panel moves, the rectangle moves with a blurred edge, deteriorating image quality.
This phenomenon is remarkable particularly when the change to intermediate luminance exists. Since dynamic images displayed on a television set, for example, use very often the intermediate luminance display, this problem is likely to occur remarkably.
Unless this problem is solved, it is difficult to apply the liquid crystal display device to television applications, and so forth.
It is an object of the present invention to provide a liquid crystal display device capable of high quality display by inhibiting the content displayed in a preceding frame from being displayed as the after-image.
It is another object of the present invention to provide a driving circuit of a liquid crystal display device capable of subjecting dynamic image portions to discriminate after-image processing.
In other words, the object of the present invention is to provide a liquid crystal display device that improves the response from the point of time at which a signal driving circuit applies a gray-scale voltage corresponding to display data to a liquid crystal panel to the point of time at which the liquid crystal panel displays the gray-scale corresponding to the gray-scale voltage so applied.
It is still another object of the present invention to provide a liquid crystal display device capable of implementing the response described above without changing the properties of liquid crystal material, and so forth.
It is still another object of the present invention to provide a liquid crystal display device that can be adapted to dynamic image display for television, etc, that very often uses intermediate luminance display.
It is a further object of the present invention to provide a liquid crystal display device having versatility without the necessity for changing an external device for outputting display data to the liquid crystal display device.
According to one aspect of the present invention, there is provided a liquid crystal display device comprising a frame memory for storing display data inputted from an external device and arithmetic operation means for comparing first display data inputted from the external device with second display data obtained by delaying by one frame the first display data stored in the frame memory, wherein correction for shortening of the response of a liquid crystal panel is applied to the display data inputted from the external in accordance with the computation result of the arithmetic operation means, and a gray-scale voltage corresponding to the data so corrected is applied to a liquid crystal panel.
In other words, the liquid crystal display device according to the present invention adds the correction data to the display data at a pixel portion at which the display content changes in correspondence with each frame, and changes the gray-scale voltage applied to the pixel portion at which the display content changes, to thereby enhance response capability of the liquid crystal display.
The above and other objects, features and advantages of the present invention will become more apparent from the detailed description of the embodiments of the invention taken in conjunction with the accompanying drawings.